The study looked at how overconfidence, representativeness bias, and risk tolerance affect investment decisions by analyzing data from 230 stock investors in Indonesia. The results showed that these psychological factors significantly influence how investors make decisions about their investments. The study suggests that investors should be cautious about relying too much on their overconfidence, biases, and risk tolerance when making investment choices. By being aware of and controlling these biases, investors can make better decisions and avoid costly mistakes. This research highlights the importance of using specific investment strategies to prevent mental errors in investment decision-making.